1. Field of the Invention
The present invention relates to a delustered thermoplastic resin composition.
2. Description of the Prior Art
Molded articles of thermoplastic resins such as vinyl chloride resin, ABS resin and acrylic resin are generally lustrous. The lusters are important properties sometimes according to the use. On the other hand, such lusters are unnecessary in other cases or, for some purposes, the lusters are unpreferred.
Conventional processes for delustering thermoplastic resins may be divided roughly into the following processes:
(1) Process wherein an inorganic or organic delustering agent is incorporated therein, and PA1 (2) Process wherein an after treatment such as delustering treatment is effected.
Process (2) is unsuitable in many cases when the fabrication is to be effected subsequently because of its poor productivity, high processing costs and insufficient delustering effect obtained, though deterioration in physical properties is small. Process (1) has a serious problem of a reduction in physical properties, though the productivity is substantially not reduced and delustering degree can be controlled according to this process and this process can be employed when the fabrication is to be effected subsequently. Particularly when an inorganic substance such as silica gel or calcium silicate is used as the delustering agent, physical properties such as impact resistance and load elongation are remarkably deteriorated and in many cases, the product thus obtained can not be used practically. On the other hand, as processes wherein an organic delustering agent, particularly, high molecular delustering agent, is used, there have been known (a) a process wherein liquid polybutadiene is used and (b) a process wherein an endopolymerization product of a mixture of cross-linked styrene/alkyl acrylate copolymer having an average particle diameter of 1-30.mu. and a non-cross-linked resin is used. The former process invites a reduction in heat distortion temperature unfavorably. As for the latter process, in fact, it is quite difficult to obtain particles of the above average diameter of 1-30.mu. by the ordinary emulsion polymerization or suspension polymerization. Further, the particles of such a size are too small to exhibit a sufficient delustering effect in the delustering treatment of ABS resin and polyvinyl chloride (PVC). In addition, the non-cross-linked resin introduced therein by the complicated endopolymerization technique reduces the delustering effect on the ABS and PVC to make the effects of the delustering agent insufficient, though the non-cross-linked resin increases compatibility thereof with ABS and PVC.
In U.S. Pat. No. 3,311,582, it is instructed to use methyl methacrylate-styrene type cross-linking polymer (this polymer may include 10% by weight or less of acrylic ester or methacrylic ester other than methyl methacrylate) having an average particle size of 0.1-0.5.mu. as an coating type delustering agent. However, such a delustering agent having an average particle size of 0.1 to 0.5.mu. is almost ineffective as a blending type delustering agent, though it is effective as a coating type delustering agent. Further, it is essential to copolymerize 10-40%, preferably 20-30% by weight of an acrylic ester with methyl methacrylate, styrene and cross-linking monomer in order to obtain an useful delustering agent.
In U.S. Pat. No. 3,345,434, it is instructed to use a cross-linked methyl methacrylate polymer or a cross-linked methyl methacrylate-acrylic ester copolymer obtained by suspension polymerization as a delustering agent. However, such a cross-linked methyl methacrylate type polymer acts ineffectively to polyvinylchloride resin etc., even if it acts effectively to methyl methacrylate type resin. In order to obtain an useful delustering agent to polyvinylchloride, it is essential to polymerize monomer mixtures composed of a major component of vinyl aromatic monomer and a minor component of acrylic ester, preferably 3 component of vinyl aromatic monomer, acrylic ester and methacrylic ester.
Generally, in the delustering agents of a type to be incorporated in a substance to be delustered, it has been said that the delustering effect thereof runs counter to compatibility thereof with the thermoplastic resin. This fact has heretofore inhibited the development of a delustering agent having both the delustering effect and physical properties-maintaining effect.